Kazuo Takayanagi

Electron-Molecule Collisions

The study of collision processes plays an important research role in modern physics. Many significant discoveries have been made by means of collision experiments. Based on theoretical, experimental, and computational studies, this volume presents an overview detailing the basic processes of electron-molecule collisions. The editors have collected papers-written by a group of international experts-that consider a diverse range of phenomena occurring in electronmolecule collisions. The volume discusses first the basic formulation for scattering problems and then gives an outline of the physics of electron-molecule collisions. The main topics covered are rotational transitions, vibrational transitions, dissociation of molecules in slow collisions, the electron-molecule collision as a spectroscopic tool for studying molecular electronic structures, and experimental and computational techniques for determining the cross sections. These well-referenced chapters are self-contained and can be read independently or consecutively. Authoritative and up-to-date, Electron-Molecule Collisions is a useful addition to the libraries of students and researchers in the fields of atomic, molecular, and chemical physics, and physical chemistry.

A generalized RPA theory of the nuclear response function

Abstract A new method of calculating the response function is proposed. The new method gives the response which is explicitly a generalization of the RPA response in a perturbative sense. When we calculate the transition amplitude of a one-body operator from the ground state to a particle-hole (p-h) state, the new response function provides all the second-order effects in addition to the first-order ones which can be obtained in the RPA theory. The new response function is obtained by the following procedure. Firstly, we consider the second RPA theory which is a generalization of the usual RPA theory. It is found that the second RPA misses some of the second-order effects. Secondly, we formulate a modified second RPA equation from the equation of motion of the operators, and then derive the p-h response function from it. It is found that the newly derived p-h response function is obtained by adding new terms to the self-energy of the p-h response function derived from the second RPA theory. Lastly, we introducd vertex functions which take into account the transitions from a particle (hole) state to a particle (hole) state. Note that the p-h response function deals with only the transition amplitudes from a particle (hole) state to a hole (particle) state.

Low-Energy Ion-Polar Molecule Collision : The Perturbed Rotational State Approach

Ion-Polar molecule collisions are studied in the Perturbed Rotational State approach. The basic idea is that the molecular rotation is nearly adiabatically deformed during the collision. The semiclassical, impact-parameter method is adopted. This formulation of the collision problem gives an easy way to calculate the rotational excitation cross sections. Numerical examples are given for the low-energy collision between a proton and a CN molecule. A scaling law is derived so that the numerical results obtained can be used also for many other collision systems.

Elementary processes involving electrons in the ionosphere

The production, slowing-down and disappearance processes of the ionospheric electrons are discussed. Emphasis is placed on the individual elementary processes, especially on electron collisions with other atmospheric constituents, rather than on other topics involving the gross structure of the real ionosphere.

Influence of the Dipole Interaction on the Low-Energy Ion-Molecule Reactions

Collision dynamics of an ion-polar molecule system is influenced considerably by the dipole interaction. The recently-developed PRS (Perturbed Rotational State) approach is applied to the problem. It is found that the ion-polar molecule reaction rate is more than ten times larger in interstellar molecular clouds than the widely-used Langevan value. A scaling law holds approximately for the effective cross section as a function of the collision energy.

The Rotational Excitation of Molecules by Slow Electrons

Publisher Summary The excitation of molecular rotation is an important energy-loss mechanism for low-energy electrons in molecular gases. When an electron beam is fired into a gas, the far-infrared emissions from rotationally excited molecules will increase. However, the expected intensity increase is too low, especially for non-polar targets, to be useful for the determination of the relevant excitation cross section. Resonance phenomena are often important in the low-energy electron scattering from atoms and molecules. These are the scattering processes through a compound state of the incident electron and the target. Two major types of resonance are usually distinguished in the electron–atom collision. One is the electron-excited resonance that corresponds to the temporary electronic excitation of the target with the incident electron captured in its field. The other is because of the temporary capture of the incident electron by the target through the adiabatic interaction. Usually the centrifugal potential barrier prevents the electron captured in the inner region of the molecular field from escaping to the outside.

Rotational and Vibrational Excitation of Polar Molecules by Slow Electrons

The excitation cross-sections for the rotational and the vibrational transitions are calculated on the basis of the Born approximation combined with the point-dipole interaction. This calculation is partly the reconfirmation and partly a slight extension of the previous treatments. The validity of this treatment is examined. It is concluded that the treatment is not applicable for the incident energies around and above 1 eV because of an effect of large distortion in the wave function of the scattered electron. Possibilities of improving the theory are briefly discussed.

Rotational Transition in Polar Molecules by Electron Collisions : Applications to CN and HCl

By the close-coupling calculation the cross sections are evaluated for rotational transitions by low energy (0.01∼10 eV) electron impact in two polar molecules, CN and HCl. The transitions from the ground state of rotation are considered and the cross sections σ( l =→ l =0), σ(0→1), σ(0→2) are calculated, l representing the rotational state of the molecule. For σ(0→1), comparison with the calculation in the Born approximation is made and it is shown that the Born results are fairly accurate even for a quite large dipole moment (at least up to 1 e a 0 , a 0 being the Bohr radius). There occurs a shape resonance in the elastic process 0→0, which may explain the peak appearing at about 10 eV of the incident energy in the measured total cross section for e -HCl collision. Finally the dependence of the calculated cross sections on the dipole moment is discussed.

A theoretical study of magnetic dipole transitions in 48Ca

Abstract Magnetic dipole transitions in 48 Ca are examined in detail by using a response function of the system. Firstly, we study the quenching phenomena of (the sum of) the transition strength B (M1)(∑ B (M1)). It is found that the second-order configuration mixing is mainly responsible for the above phenomena and the exchange currents including the Δ-hole also play an important role. Secondly, we study the form factor of the collective magnetic dipole transition to the state at E x = 10.2 MeV. The effects of the (second order) configuration mixing and the exchange currents on the form factor are discussed.

Medium corrections in intermediate-energy nucleon-nucleus scattering

Abstract Medium corrections in elastic and inelastic nucleon-nucleus scattering are discussed in the framework of Watsons multiple scattering theory. We derive formulae for the effective interactions to be used in the calculation of elastic and inelastic scattering based on a consistent local-density approximation. We show the numerical results of analyses of the p + 16 O reaction at E p = 135 MeV.